Method of improving tissue paper softness

ABSTRACT

IMPROVED SOFTNESS, SURFACE SMOOTHNESS AND LIMPNESS IN TISSUE PAPER IS ATTAINED WITH A MINIMUM OF TISSUE PAPER SHEET STRENGTH LOSS. THE TRAVELING TISSUE PAPER, THAT IS CREPED WADDING, IS SUBJECTED TO A NIP BETWEEN A BRUSH ROLL AND A PATTERNED BACKING ROLL AT CONTROLLED RELATIVE SPEEDS OF THE SHEET, PATTERNED BACKING ROLL AND BRUSH. THE SHEET SPEED IS LESS THAN THE PERIPHERAL SPEED OF THE BRUSH ROLL BUT GREATER THAN THAT OF THE BACKING ROLL SO THAT THE SHEET IS WORKED BY THE BRUSH AND PATTERNED BACKING ROLL AS IT SLIPS RELATIVE TO THE PATTERNED BACKING ROLL.

y 3, 1971 E. R. WAND METHOD OF IMPROVING TISSUE PAPER SOFTNESS 2 Sheets-Sheet 1 Filed June 27, 1969 United States Patent 3,592,732 METHOD OF IMPROVING TISSUE PAPER SOFTNESS Edwin R. Wand, Appleton, Wis., assignor to Kimberly- Clark Corporation, Neenah, Wis. Filed June 27, 1969, Ser. No. 837,256 Int. Cl. D21f 11/00 US. Cl. 162-197 9 Claims ABSTRACT OF THE DISCLOSURE worked by the brush and patterned backing roll as it slips relative to the patterned backing roll.

This present invention relates to novel, soft, limp,

lightweight tissue paper sheets and to improved methods for producing the same. More specifically, the invention is directed to brushed tissue paper products manufactured by procedures which permit the attainment of softness, surface smoothness and limpness with a minimum of paper sheet strength loss.

It is known to provide paper with a velvety surface condition by effecting a raising of the fibers of the web. Such has been accomplished to a degree by picking, fiutfing or brushing actions. Such procedures have suffered from a number of drawbacks including particularly the control of results, non-uniformity being a prevalent factor in prior art products.

A primary object of the present invention is to provide tissue paper of improved softness, limpness and surface smoothness by a novel procedure and with only minimal loss of sheet strength.

I have found that lightweight tissue paper sheets may be adequately worked to provide a soft, limp, smooth sheet of good strength by subjecting the paper sheet to a nip formed between a brush roll and patterned backing roll and imparting a certain speed relationship to the tissue sheet, the backing roll and the brush. Generally speaking, an important finding characteristic of my process is that the backing roll should be driven at a lower peripheral speed than the sheet and the sheet preferably is at a considerably slower speed than the peripheral speed of the brush roll. Also, I have found that, using a patterned backing roll, the larger the sheet speed relative to the backing roll the greater is the softness attained; additionally, surface smoothness is more readily achieved by moving the brush roll also at high speeds relative to the patterned backing roll, in general two or three to ten times the patterned backing roll speed.

The invention will be more fully understood by reference to the following description of preferred embodiments of the invention and the accompanying drawings wherein:

FIG. 1 is a schematic drawing of the side elevation of equipment for carrying out a preferred embodiment of the process of invention;

FIG. 2 is an enlarged, partial and edge view of a tissue sheet in a nip between a brush roll and a backing roll particularly illustrating the sheet flexure in the nip;

FIG. 3 is a view taken on line 33 of FIG. 2 but enlarged about four times over the FIG. 2 showing and particularly illustrating the action of the brush bristles at the protrusions; and

FIG. 4 is a view taken on line 4--4 of FIG. 3 further illustrating the relation of brush bristles and backing roll.

Referring now more particularly to the drawing, I have shown in FIG. 1 a sheet or web l of wood fiber material being drawn from a supply roll 2 and passing through nip 3 formed by backing roll 4 and brush roll 5 to windup at 6. Windup rolls 7, 8 rotating in the directions indicated by the arrows support the roll 6 and provide for the winding of the roll in conventional manner.

The sheet 1 is a single ply of creped cellulosic wadding of about 9 pounds per 2880 sq. ft. dryer basis weight and having a crepe ratio of about 1.20. The sheet was formed by weight of about bleached sulfite pulp, 40% northern kraft and 10% unbleached sulfite. This sheet had an initial tensile strength in the longitudinal direction of about 1008 grams per 3" width and in the cross direction of about 320 grams per 3" width. The sheet had a bulk density of 1.74 grams per cubic inch, a harshness level of 9.0 at a stiffness of 5.5, and a stretch of 26%.

Stiffness and harshness are measured by comparison with known standards and rated on a scale of value of l to 10; in each instance a lower value indicates less stiffness or less harshness, that is, generally a greater degree of limpness or of softness.

The supply roll 2, the backing roll 4 and brush roll 5 are independently driven "by conventional means (not shown) in the directions indicated by the arrows.

Supply roll 2 is suitably independently driven to prevent stretching of the sheet 1 and, when so driven, the speed of windup at 6 is correlated with the speed of withdrawal. The web speed may be adjusted within a limited speed range between that of the backing roll and the brush roll by varying the tension applied by the unwind roll 2 and the windup roll 6.

Backing roll 4 as shown in FIGS. 1 to 4 is a common type of male embossing roll having pegs 10 uniformly disposed about the roll periphery and also having a shaft 12. As shown (FIG. 3) pegs 10 are of circular configuration and well spaced apart, the pegs having a diameter of about 0.060" and being spaced on centers about 0.110". The roll diameter in this instance is about 10".

Brush roll 5 is suitably about 7 /2" in diameter and preferably has relatively soft bristles, rows of which are indicated at 9 and 9A. The use of soft bristles provides for uniform brush pressure against the traveling sheet 1 and for minimizing of paper strength loss in the softening operation. The brush acts to urge the sheet against the backing roll 4 into depressed zone 11 between egs or knurlings 10 and to maintain the sheet in contact with the pegs as the sheet slides on the periphery of the backing roll 4 against the sides of the pegs and peg edges as illustrated in FIGS. 3 and 4. By pressing of the sheet as the sheet slides on the backing roll, the surface fibers of the sheet are largely released from each other and the body of the sheet to create softness to the touch while, simultaneously, the sheet is worked in the depressed zones 11 to break the so-called hydrogen or fiber bonds and provide limpness in the sheet. A very suitable brush roll for the purpose has bristles about long, very closely packed and of about 0.008 diameter. Such is illustrative only, however, as the brush roll may vary widely depending upon the specific results desired; in general, increasing bristle stiffness tends to cause greater paper strength loss although such may be offset by higher brush speeds relative to the backing roll speed. Contrariwise, higher brush speeds tend to result in shorter bristle life due to the fatigue caused by the more rapid flexing action occurring at higher speeds.

In the practice of the invention employing the specific sheet and arrangement described, the sheet is directed at a speed of about 1450 f.p.m. to the nip 3. The peripheral speed of the backing roll is 1230 f.p.m. and that of the brush roll 3700 f.p.m. Under this speed relationship the sheet is readily urged by the brush into the depressed zones 11 and the sheet slides against the lower moving pegs as the sheet leaves the backing roll. Viewed somewhat differently, the backing roll exerts a drag on the sheet. The combined effect is the production of limpness in the sheet, fiber upsetting resulting in sheet smoothness and softness by the action of the bosses and softening by the action of the brush on the side of the sheet opposite the backing roll.

The sheet product has a final tensile in the longitudinal direction of about 808 grams per 3" width, in the cross direction of about 218 grams per 3" width; sheet bulk density is 1.83 gram per cubic inch, and the harshness value 6.0 at a stiffness value of 1.0. Thus, a much more limp sheet of greater softness at small strength loss has been provided.

Importantly, no significant embossing of the sheet oc- L curs; if an embossed product is desired, usual embossing procedures may be employed on the softened product.

Various modifications are applicable to the specific apparatus and specific mode of operation described. The

backing roll may have a wide variety of patterns and, for

the handling of very weak webs where sheets fiber debonding to attain limpness is not a major factor, the pattern depth may be minimal; conversely, for tightly bonded sheets the depth of the bosses should be greater.

The brush roll need not be a bristle roll but may be of any type capable of picking on fluffing the fiber surface including wire rolls, toothed rolls and the like.

As already indicated, the speed relationships are of utmost importance, and I consider the speed of the backing roll relative to sheet speed and brush roll speed to r be critical. The backing roll peripheral speed must be less than the sheet speed to provide for sliding of the sheet relative to the backing roll. In general, I prefer to pass the sheet across the backing roll at a differential speed of about 200 f.p.m.; a decrease in this differential results in a somewhat stiffer product and, conversely, greater speed differentials tend towards more limp materials; a differential of between about 75 f.p.m. and 300 f.p.m. is quite satisfactory for most purposes, and the peripheral speed ranges under such conditions may be between about 425 f.p.m. and 1425 f.p.m. for the backing roll and 500 f.p.m. and 1500 f.p.m. for the sheet speed. Under these generally stated conditions I prefer to have the brush roll operate at approximately one and a half (1 /2) to two and a half (2 /2) times sheet speed, that is, between about 750 f.p.m. and 3750 f.p.m., a useful normal brush speed being about 3700 f.p.m.

The pressure exerted by the bruh roll influences the limpness of the product, the limpness increasing with pressure and with the pattern depth of backing roll To obtain surface smoothness, the pressure and pattern depth may be minimal and such conditons are useful when smoothness and softness are desired at low paper strength loss.

While the foregoing disclosure has emphasized a relief or male backing roll, an intaglio roll having a multiplicity of cells also presents to a web depressions between relatively raised areas and serves a similar purpose to the relief type backing roll. To inhibit cutting of the traveling web, the cell boundaries should be well smoothed.

It is thus seen that a number of factors influence the character of the specific sheet but, in all cases, I have found that maintaining backing roll speed low relative to sheet and brush roll speeds is the important determining factor in permitting softness while maintaining other desirable sheet properties.

As many apparently widely different embodiments of this invention may be made without departing from the spirit and scope thereof, it is to be understood that I do not limit myself to the specific embodiments thereof except as defined in the appended claims.

I claim:

1. The method of producing a soft, limp, lightweight tissue paper sheet by a working of the tissue paper while it is traveling on a backing roll, the steps in combination of driving a brush roll and a patterned backing roll in opposite rotational directions such that the peripheral speed of the brush roll exceeds that of the backing roll, and directing a lightweight tissue paper sheet through a nip formed by the brush roll and backing roll at a speed which is less than the peripheral speed of the brush roll so that the surface of the sheet is worked by the brush roll but at a speed greater than the peripheral speed of the backing roll so that the sheet slips relatively to the backing roll.

2. The method according to claim 1 in which the backing roll is a patterned roll having male bosses and the sheet speed relative to the roll is such that the brush bristles urge the sheet into contact with sides of the bosses and simultaneously effect a breaking down of paper bonds at the bosses but without significant embossment of the traveling sheet.

3. The method according to claim 2 in which the peripheral speed of the brush roll relative to the peripheral speed of the backing roll is about 2 to 10.

4. The method according to claim 1 in which the patterned backing roll has depressions between raised areas and working of the sheet is effected in the depressed and raised areas of the roll as the sheet Slips over the backing roll through the depressions.

5. The method according to claim 1 in which the brush roll has a peripheral speed of between about 750 f.p.m. and 3750 f.p.m., the backing roll has a peripheral speed of between about 425 f.p.m. and 1425 f.p.m., and the sheet has a speed of between about 500 f.p.m. and 1500 f.p.m., the ratio of the speed of the brush roll to the backing roll being in the range of 2 to 10.

6. The method according to claim 5 in which the peripheral speed of the brush roll in f.p.m. is between about 1 /2 to 2 /2 times the sheet speed in f.p.m.

7. The method according to claim 5 in which the speed of the sheet is greater than the peripheral speed of the backing roll and the differential is between and about 300 f.p.m.

8. The method according to claim 7 in which the said differential speed is about 200 f.p.m.

9. The method according to claim 1 in which the brush roll has a peri heral speed of about 3700 f.p.m., the backing roll has a peripheral speed of about 1230 f.p.m. and the sheet has a linear speed of about 1450 f.p.m.

References Cited UNITED STATES PATENTS 860,696 7/1907 Scherf 162-27l 2,950,223 8/1960 Bletzinger et a1. 162117X 3,101,520 8/1963 George et a1 28l S. LEON BASHORE, Primary Examiner T. G. SCAVONE, Assistant Examiner US. Cl. X.R. 

